1. Field of the Invention
The present invention relates to an impact drill for use in a drilling operation on a concrete, mortar or tile, for example, and more particularly to an impact drill having a drill mode for performing a drilling operation by rotating a drill bit and an impact drill mode for performing a drilling operation by rotating and vibrating the drill bit.
2. Description of the Related Art
FIG. 1 shows a conventional example of the impact drill of this kind. In FIG. 1, reference numeral 1 denotes a main frame portion that forms an outer shell of the impact drill and has the self-contained parts at predetermined positions, comprising a gear cover 17, an inner cover 18, an outer cover 19, a housing 7 and a handle portion 6. Reference numeral 2 denotes a spindle inserted transversely through the gear cover 17, and 3 denotes a drill chuck attached at the top end of the spindle. A rotational ratchet 4 is mounted near the central part of the spindle 2. The rotational ratchet 4 is rotated along with the rotation of the spindle 2, and moved along with the axial movement of the spindle 2. The serrated irregularities are formed on one face 4a of the rotational ratchet 4.
Reference numeral 5 denotes a stationary ratchet disposed at a position opposed to the rotational ratchet 4, in which the serrated irregularities are also formed on one face 5a of the stationary ratchet. The stationary ratchet 5 has a hollow cylindrical shape, and is fixed to the inner cover 18, irrespective of the rotation and axial movement of the spindle 2.
On the other hand, a motor 8 is disposed inside the housing 7 linked to the handle portion 6. A rotational driving force of the motor 8 is transmitted via a rotation shaft 9 to a gear 10. Since the gear 10 is press fit into a second pinion 11, the rotational driving force is transmitted to the second pinion 11. The second pinion 11 has two pinion portions 11a, 11b having a different number of teeth, which are engaged with a low speed gear 12 and a high speed gear 13, respectively. When the second pinion 11 is rotated, both the gears 12, 13 are also rotated.
Reference numeral 14 denotes a clutch disk engaged with the spindle 2 and mounted to be slidable in the axial direction. If the clutch disk 14 is inserted into a concave portion of the low speed gear 12, the rotation of the second pinion 11 is transmitted via the low speed gear 12 and the clutch disk 14 to the spindle 2, as shown in FIG. 1. On the other hand, if the clutch disk 14 is slid to the right from the position of FIG. 1, and inserted into a concave portion of the high speed gear 13, the rotation of the second pinion 11 is transmitted via the high speed gear 13 and the clutch disk 14 to the spindle 2. Accordingly, the spindle 2 can be rotated at low speed or high speed by movement of the clutch disk 14.
Reference numeral 15 denotes a change lever for changing the operation mode of the impact drill, namely, between a drill mode and an impact drill mode. A change shaft 16 is press fit into the change lever 15, whereby when the change lever 15 is rotated, the change shaft 16 is also rotated. The change shaft 16 has a notch portion 16a, as shown in FIGS. 2, 3 and 4, whereby when the notch portion 16a is at the position of FIG. 2, the impact drill is operated in the drill mode, while when the notch portion 16a is at the position of FIG. 3, the impact drill is operated in the impact drill mode.
(A) Drill Mode
When a drill bit (not shown) attached in the drill chuck 3 is contacted with a machined surface and the handle portion 6 is pressed in a direction of the arrow in FIG. 1, an end part of the spindle 2 makes contact with the change shaft 16 to be immovable to the right, when the notch portion 16a of the change shaft 16 is at the position of FIG. 2. Accordingly, there is no contact between the irregular face 4a of the rotational ratchet 4 and the irregular face 5a of the stationary ratchet 5. Accordingly, a rotational driving force of the motor 8 is transmitted via the low speed gear 12 or high speed gear 13 to the spindle, so that the drill bit is given a rotational force.
(B) Impact Drill Mode
In an impact drill mode, the notch portion 16a of the change shaft 16 is brought into the position of FIG. 3 by rotating the change lever 15. Then, the drill bit attached in the drill chuck 3 is contacted with a machined surface. If the handle portion 6 is pushed in a direction of the arrow in FIG. 1, an end part of the spindle 2 enters the notch portion 16a, as shown in FIG. 4. That is, the spindle 2 is slightly moved to the right, so that the irregular face 4a of the rotational ratchet 4 is contacted with the irregular face of the stationary ratchet 5.
In drilling the machined surface, if the spindle 2 is rotated in the state of FIG. 4, the rotational ratchet 4 is meshed and engaged with the stationary ratchet 5, and rotated to cause vibration due to the irregular faces of both the ratchets 4 and 5. This vibration is transmitted through the spindle 2 to the drill bit (not shown). That is, the drill bit is given a rotational force and vibration to perform a drilling operation.
However, when the impact drill is operated in the impact drill mode, the vibration caused by rotation of the spindle in the state where the irregular faces of the ratchets 4 and 5 are contacted under pressure is transmitted not only to the drill bit, but also through the stationary ratchet 5 and the inner cover 18 from the housing 7 to the handle portion 6. Therefore, there is a problem that the user of the impact drill undergoes a great vibration, and feels uncomfortable. Especially when the impact drill is continuously employed for a long time, care must be taken not to transmit the vibration to the user and cause adverse effect on the health of the user.
Several proposals for reducing the vibration transmitted to the user have been made. For example, in JP-UM-B-2-30169, a structure was disclosed in which a clutch cam 22 is supported movably in the axial direction of the spindle 20, and pressed and urged to a rotary cam 21 by a spring 23, as shown in FIG. 5. In FIG. 5, reference numeral 21 denotes a rotary cam that is rotated along with the spindle 20. A cam face 21a of the rotary cam 21 is formed with serrated irregularities.
On the other hand, the clutch cam 22 is composed of a hollow cylindrical portion slidable in the axial direction of the spindle 20 and a flange portion 22b. A cam face 22c of the flange portion 22b is formed with a serrated irregular face.
The spring 23 is provided between the flange 22b of the clutch cam 22 and a plate 24a engaging a groove 22a of the clutch cam 22, and always urges the clutch cam 22 toward the rotary cam 21. Thus, when the spindle 20 is moved backward, the cam faces 21a and 22c are contacted under pressure. If a pressing force applied to the spindle 20 overcomes a resilient force of the spring 23, the spring 23 is compressed, so that the clutch cam 22 is moved backward (to the right in the figure). When the clutch cam 22 is moved forward from the back position due to a resilient force of the spring 23, it strikes against the rotary cam 21, so that the rotary cam 21 is vibrated together with the spindle 20.
With this structure, since the vibration caused by contact between the cam faces 21a and 22c is relieved by the spring 23 and transmitted to the handle portion (not shown), there is the effect that the vibration transmitted to the user is reduced as compared with the structure in which the ratchet 5 is firmly disposed as shown in FIG. 1.
On the other hand, FIGS. 6 and 7 are schematic views showing the above structure in which the change shaft 16 and the change lever 15 as shown in FIGS. 2, 3 and 4 are disposed at the right end portion of the spindle 20 as shown in FIG. 5. In FIGS. 6 and 7, a spring 25 is additionally inserted between the rotary cam 21 and the plate 24a to prevent the spindle 20 from being moved to the right.
When the notch portion 16a of the change shaft 16 is at the position as shown in FIG. 6, the impact drill is operated in the drill mode in which the cam faces 21a and 22c are always out of contact. Also, when the notch portion 16a of the change shaft 16 is at the position as shown in FIG. 7, the impact drill is operated in the impact drill mode in which the cam faces 21a and 22c are contacted and collided.
In this impact drill mode, if a pressing force is applied to the main body (not shown), the spindle 20 is moved to the right. However, when the pressing force is weak, a right end portion of the spindle 20 slightly enters the notch portion 16a, and the cam faces 21aand 22c of FIG. 7 are lightly contacted, so that the back movement amount of the clutch cam 22 is small, the restoring force of the spring 23 is small, and a stroke force from the clutch cam 22 to the rotary cam 21 is reduced.
On the other hand, when the pressing force is strong, a right end portion of the spindle 20 deeply enters the notch portion 16a, and the cam faces 21a and 22c are greatly engaged, so that the clutch cam 22 is greatly moved backward, whereby the restoring force of the spring 23 is great, and the stroke force from the clutch cam 22 to the rotary cam 21 is significant.
Herein, when an object to be drilled which is hard and thin tile or concrete is positioned for drilling, or drilled prudently, it is necessary to sustain a state where the pressing force is weakened to suppress the stroke force, as described above. Several proposals have been conventionally made for the structure in which the magnitude of stroke force is adjustable.
In Japanese Patent No. 3002284, the maximal movement amount of the rotational ratchet and the spindle is made larger than engageable with the stationary ratchet, in which the stationary ratchet is provided movably in the axial direction, and biased forward by the spring. A biasing force of the spring is adjusted by changing a force for pressing the main body.
In JP-A-62-74582, there was described an impact drill in which the rotational ratchet and the spindle can not be moved in the axial direction, and the stationary ratchet is provided movably in the axial direction, and biased forward by the spring, whereby a member for regulating the axial movement of the stationary ratchet is provided adjustably from the outside. The stationary ratchet is regulated from moving forward beyond a predetermined position by adjusting the regulating member, so that the intermeshing depth of ratchets is adjusted.
In Japanese Patent No. 2754047, there was described an impact drill in which the rotational ratchet and the spindle can not be moved in the axial direction, and the stationary ratchet is provided movably in the axial direction, and biased forward by the spring, whereby a second spring for adjusting the compression amount from the outside is provided, in addition to a first spring for always biasing the stationary ratchet. By adjusting the compression amount from the outside, a combination of the first spring and the second spring is varied to adjust the biasing force of the spring.
In JP-A-3-178708, there was described an impact drill in which the rotational ratchet and the spindle are provided to be movable backward to the position at which they are engaged with the stationary ratchet, and the stationary ratchet is provided movably in the axial direction, and biased forward by the spring, whereby the axial position of a spring seat is provided adjustably from the outside. The biasing force of the spring is adjusted by moving the spring seat from the outside. Also, there was described a similar impact drill in which the length of an outer frame itself is provided adjustably. In this case, the biasing force of the spring is adjusted by changing the length of the outer frame itself.
In JP-A-4-240010, there was described an impact drill in which the rotational ratchet and the spindle are provided to be movable backward to the position at which they are engaged with the stationary ratchet, and the stationary ratchet is provided movably in the axial direction, and biased forward by the spring, whereby the axial position of a seat accepting the spring from behind is provided adjustably from the outside. The biasing force of the spring is adjusted by changing the axial position of the seat accepting the spring from behind.